Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean
More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000–6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chem...
Published in: | Geochimica et Cosmochimica Acta |
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Main Authors: | , , , , , |
Format: | Article in Journal/Newspaper |
Language: | unknown |
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PERGAMON-ELSEVIER SCIENCE LTD
2014
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Subjects: | |
Online Access: | https://epic.awi.de/id/eprint/35447/ https://epic.awi.de/id/eprint/35447/2/Lechtenfeld2014.pdf https://hdl.handle.net/10013/epic.43428 https://hdl.handle.net/10013/epic.43428.d002 |
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Open Polar |
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Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) |
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ftawi |
language |
unknown |
description |
More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000–6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from −229‰ to −495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to ~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment (“island of stability”). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 μM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, representing average surface water DOM ages of 4920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index IDEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate. |
format |
Article in Journal/Newspaper |
author |
Lechtenfeld, Oliver J. Kattner, Gerhard Flerus, Ruth McCallister, S. Leigh Schmitt-Kopplin, Philippe Koch, Boris P. |
spellingShingle |
Lechtenfeld, Oliver J. Kattner, Gerhard Flerus, Ruth McCallister, S. Leigh Schmitt-Kopplin, Philippe Koch, Boris P. Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
author_facet |
Lechtenfeld, Oliver J. Kattner, Gerhard Flerus, Ruth McCallister, S. Leigh Schmitt-Kopplin, Philippe Koch, Boris P. |
author_sort |
Lechtenfeld, Oliver J. |
title |
Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
title_short |
Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
title_full |
Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
title_fullStr |
Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
title_full_unstemmed |
Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean |
title_sort |
molecular transformation and degradation of refractory dissolved organic matter in the atlantic and southern ocean |
publisher |
PERGAMON-ELSEVIER SCIENCE LTD |
publishDate |
2014 |
url |
https://epic.awi.de/id/eprint/35447/ https://epic.awi.de/id/eprint/35447/2/Lechtenfeld2014.pdf https://hdl.handle.net/10013/epic.43428 https://hdl.handle.net/10013/epic.43428.d002 |
geographic |
Southern Ocean Weddell Weddell Sea |
geographic_facet |
Southern Ocean Weddell Weddell Sea |
genre |
Southern Ocean Weddell Sea |
genre_facet |
Southern Ocean Weddell Sea |
op_source |
EPIC3Geochimica et Cosmochimica Acta, PERGAMON-ELSEVIER SCIENCE LTD, 126, pp. 321-337, ISSN: 0016-7037 |
op_relation |
https://epic.awi.de/id/eprint/35447/2/Lechtenfeld2014.pdf https://hdl.handle.net/10013/epic.43428.d002 Lechtenfeld, O. J. , Kattner, G. , Flerus, R. , McCallister, S. L. , Schmitt-Kopplin, P. and Koch, B. P. orcid:0000-0002-8453-731X (2014) Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean , Geochimica et Cosmochimica Acta, 126 , pp. 321-337 . doi:10.1016/j.gca.2013.11.009 <https://doi.org/10.1016/j.gca.2013.11.009> , hdl:10013/epic.43428 |
op_doi |
https://doi.org/10.1016/j.gca.2013.11.009 |
container_title |
Geochimica et Cosmochimica Acta |
container_volume |
126 |
container_start_page |
321 |
op_container_end_page |
337 |
_version_ |
1766206380176310272 |
spelling |
ftawi:oai:epic.awi.de:35447 2023-05-15T18:25:09+02:00 Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean Lechtenfeld, Oliver J. Kattner, Gerhard Flerus, Ruth McCallister, S. Leigh Schmitt-Kopplin, Philippe Koch, Boris P. 2014-02-01 application/pdf https://epic.awi.de/id/eprint/35447/ https://epic.awi.de/id/eprint/35447/2/Lechtenfeld2014.pdf https://hdl.handle.net/10013/epic.43428 https://hdl.handle.net/10013/epic.43428.d002 unknown PERGAMON-ELSEVIER SCIENCE LTD https://epic.awi.de/id/eprint/35447/2/Lechtenfeld2014.pdf https://hdl.handle.net/10013/epic.43428.d002 Lechtenfeld, O. J. , Kattner, G. , Flerus, R. , McCallister, S. L. , Schmitt-Kopplin, P. and Koch, B. P. orcid:0000-0002-8453-731X (2014) Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean , Geochimica et Cosmochimica Acta, 126 , pp. 321-337 . doi:10.1016/j.gca.2013.11.009 <https://doi.org/10.1016/j.gca.2013.11.009> , hdl:10013/epic.43428 EPIC3Geochimica et Cosmochimica Acta, PERGAMON-ELSEVIER SCIENCE LTD, 126, pp. 321-337, ISSN: 0016-7037 Article isiRev 2014 ftawi https://doi.org/10.1016/j.gca.2013.11.009 2021-12-24T15:39:29Z More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000–6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from −229‰ to −495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to ~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment (“island of stability”). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 μM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, representing average surface water DOM ages of 4920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index IDEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate. Article in Journal/Newspaper Southern Ocean Weddell Sea Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) Southern Ocean Weddell Weddell Sea Geochimica et Cosmochimica Acta 126 321 337 |